Majority carrier rectifying barrier diodes are known. Among them are the so-called planar doped barrier (PDB) diodes. See, for instance, U.S. Pat. No. 4,410,902, which discloses a semiconductor diode comprising a n.sup.+ -i-p.sup.+ -i-n.sup.+ layer structure, with the p.sup.+ layer being very thin. Modifications of the structure of the '902 patent are also known. See, for instance, British patent application GB 2,221,091A, which discloses a semiconductor diode having a n.sup.+ -n-i-p.sup.+ -i-n-n.sup.+ layer structure, with the two n-layers differing in their dopant concentration and, optionally, in their thickness. The '091A application also discloses that the i-layers can be lightly n-doped in order to reduce device resistance, and that either, but not both, of the i-layers could be omitted. See also U.S. Pat. No. 4,839,709, which discloses a diode having n-p-i-n layer structure, and U.S. Pat. No. 4,149,174, which discloses a diode having a n.sup.+ -p-n layer structure. In all these exemplary diodes the thickness of the acceptor-doped region is selected such that the region is substantially depleted of holes.
PDB diodes (including all modifications of the diode of the '902 patent; we will refer to these devices collectively as "PDB" diodes) generally have advantageous characteristics that make them attractive for microwave applications, e.g., microwave mixers or detectors. These diodes typically comprise III-V semiconductor material (typically GaAs), with Be being the acceptor dopant species. See, for instance, M. J. Kearney et al, GEC Journal of Research, Vol. 8(1), p. 1, 1990.
Although prior art PDB diodes have many advantageous features, it has to date proven difficult to manufacture these devices with high yield, and we are unaware of any suggestions in the prior art regarding the source of, or a solution to, this problem. In view of the commercial potential of PDB diodes, it would be highly desirable to have available a design that can more readily and reliably be manufactured to meet typical design specifications. This application discloses such a design.
The p-dopant in n-p-n AlGaAs/GaAs heterojunctive bipolar transistors (HBTs) has conventionally been Be. Recently, it has been disclosed that carbon is a promising p-dopant for these HBTs, due at least in part to the relatively small diffusion coefficient of carbon in GaAs. See, for instance, T. Makimoto et al., Applied Physics Letters, Vol. 54(1), p. 39. However, T. Nozu et al., Proceedings of the GaAs IC Symposium, Miami Beach, Fla., Oct. 5-7, 1992, p. 157, discloses that no serious Be diffusion occurs in AlGaAs/GaAs HBTs with Be-doped base, provided the growth temperature is below 620.degree. C. All the above cited references are incorporated herein by reference.
Carbon-doped GaAs has been produced by a variety of growth techniques, including chemical beam epitaxy (see, for instance, T. H. Chiu et al., Applied Physics Letters, Vol. 57(2), p. 171), metalorganic molecular beam epitaxy (e.g., C. R. Abernathy et al., Applied Physics Letters, Vol. 57(3), p. 294) and molecular beam epitaxy (e.g., R. J. Malik et al., Applied Physics Letters, Vol. 53(26), p. 2661. The latter paper discloses an advantageous doping technique, namely, carbon sublimation from a heated graphite filament. See also U.S. Pat. No. 5,106,766.